Aqueous slurry-type blasting compositions containing a hexamethylene-tetramine nitrate sensitizer



3 3.18 74d AQUEIUUS SLURRY-TYPI E ELASTKNG CUMPGSH- 'llllN C(ONTAiNllNG A HEXAMETHYLENE- TETRAll HNE NHTRATE SEl ElTiZER Harry R. Fee, Hopatcong, NJL, and Robert W. Lawrence, Wilmington, Del, assignors to Hercules incorporated, Wilmington, Del a corporation of Delaware No Drawing. Filed July 12, 1966, er. No. 564,555

ill Claims. ('Cl. 149-38) This invention relates to inorganic oxidizer salt-type blasting compositions of the aqueous slurry type containing selected hexamethylenetetramine nitrates as sensitizer components.

Inorganic oxidizer salt blasting compositions of the aqueous slurry type have had wide use in the explosives industry in recent years. These compositions comprise an inorganic oxidizer salt, water, a sensitizer, and, generally, a thickening agent in at least an amount to impart sufiicient consistency to the slurry to prevent settling of any of the various ingredients.

Various sensitizer materials have been utilized in these compositions, including smokeless powder as disclosed and claimed in US. 3,235,425, and particulate metals and high explosives, such as TNT and/or aluminum as disclosed and claimed in US. 2,930,685.

This invention is concerned with new inorganic oxidizer salt blasting compositions of the aqueous slurry type containing a nonexplosive sensitizer component, alone or in conjunction with a supplemental sensitizer.

In accordance with the invention, inorganic oxidizer salt explosive compositions of the aqueous slurry type are provided which contain, a sensitizing amount, generally from 1 to 18 weight percent, or any suitable amount outside that range, of a sensitizer component selected from the group consisting of hexamethylenetetramine mononitrate, hexamethylenetetramine dinitrate, and mixtures of said nitrates. The compositions of the invention generally comprise (Weight basis) from 8 to 25 percent water, from 40 to 85 percent of an inorganic oxidizer salt, the above-described sensitizer component, and a thickener, the latter usually in an amount of from 0.2 to percent.

By the term inorganic oxidizer salt, as is well known in the explosives art, is meant one which under the conditions of the detonation liberates oxygen for the degree of oxygen balance required.

In accordance with now preferred practice, hexamethylenetetramine mononitrate, (CH N -HNO also referred to hereinafter as HMTAMN, as the sensitizer, is incorporated into the blasting composition as aqueous product of reaction of 1 mol ammonium nitrate, 1 mol ammonia and 6 mols formaldehyde, the water content of the aqueous product contributing to the overall water content of the finished composition. The practice of this embodiment imparts a pH to the resulting explosive composition mixture, on the acid side, which is especially advantageous from the standpoint of the desired degree of cross-linking of the now preferred guar gum thickener and of stability of the resulting cross-linked product (gel) that can be obtained under those pH conditions.

Although the blasting compositions of the invention contain the amine nitrate sensitizer in proportions as low as about 1 percent, it is generally preferred that when said amine nitrate is present in an amount less than about 5 percent, a supplemental sensitizer also be present. However, it is within the scope of the invention to supplement the amine nitrate sensitizer, independently of its content, as desired. Any suitable known sensitizer material, in the order of, for example, from 2 to 25 weight percent of the finished composition, can be utilized as a supplemental sensitizer in the practice of the invention, exemplary of which are aluminum, magnesium- 33%,740 Patented May 9, T1967 aluminum alloys, and coal, all in finely divided form, hydrocarbon oils, and the like-aluminum in at least partially flake form being now preferred.

Now preferred compositions of the invention contain (weight basis) from 12 to 20 percent water, from 5 to 14 percent of the amine nitrate sensitizer, generally HMTAMN, from to 65 and from 5 to 20 percent, respectively, of ammonium nitrate and sodium nitrate as the oxidizer salt, and from 0.5 to 2.0 percent guar gum generally in cross-linked form, as a thickener.

Although ammonium nitrate alone, or with sodium nitrate, is in most instances the inorganic oxidizer salt component, other inorganic oxidizer salts can be used, alone or with ammonium nitrate as a supplementary oxidizer salt, the alkali metal nitrates being now preferred. Generally, when ammonium nitrate is utilized with a supplementary salt, it comprises a major proportion of the total oxidizer salt, i.e., at least percent of the total. Exemplary inorganic oxidizer salts that can be used alone, or together with ammonium nitrate, are alkali metal and alkaline earth metal nitrates and perchlorates (including ammonium) as, for example, sodium nitrate, magnesium nitrate, calcium nitrate, potassium nitrate, barium nitrate, sodium perchlorate, ammonium perchlorate, calcium perchlorate and magnesium perchlorate.

Particle size and type of the oxidizer salt ingredient are not generally critical. For example ammonium nitrate can consist of prill such as used in fertilizers and which are substantially all on 20 mesh, or it can be granular and in that form, vary from coarse to fine. Other oxidizer salt ingredients are generally of comparable particle size. However, when desired, any or all of the oxidizer salt component can be added to the formulation in aqueous solution.

The amount of thickener is dependent upon the particular thickener and the desired consistency of the finished composition. Generally, a thickener content up to about 5 percent and more often not exceeding about 2 percent is sufficient. When the thickener content is within the range of 0.2 to 0.5 percent, there is generally sufficient thickening to prevent settling of the composition ingredients, although additional thickener is often required in order to impart a satisfactory degree of cohesiveness so that the composition retains its form as a unit mass, preferably plastic but deformable. Exemplary thickeners are sodium carboxymethylcellulose, karaya gum, water-soluble starches, locust bean meal, cereal products and the like.

The compositions of the invention are generally insensitive to detonating action of a No. 8 commercial blasting cap but are, in all events, detonatable by conventiontl booster charges of PETN (pentaerythritol tetranitrate), RDX (cyclotrimethylenetrinitramine), Pentolite (PETN- TNT, 50/50), tetryl, Composition B (RDXTNT /40) and the like. One booster advantageously employed is a dispersion of a crystalline high explosive, e.g., FETN or RDX in a plastic carrier such as described in US. 2,965,466, and which is detonated by either a commercial blasting cap or a detonating fuse. A now preferred booster comprises a cast cylindrical body of capand fuse-insensitive explosive, and a tube assembly within the cast body, containing cap-sensitive crystalline high explosive together with structure for support of initiator means therefor, as disclosed and claimed in US. 3,212,438.

In preferred practice, the explosive compositions of the invention are of the well-known class of nitrocarbonitrates, by which term it is meant there are no sensitizers which in themselves are high explosives, and the mixtures will not detonate with a No. 8 blasting cap when packed for shipment.

The invention is illustrated with reference to the following formulations, all on a weight percent basis.

l portion of oxidizer salt with agitation to form the final product. The last added guar gum is in inhibited form,

TABLE Formulation 1 2 3 4 5 i 6 l 7 i 8 i 9 i 10 Water a. 17. 8 18.0 15. 5 15. 5 15. 4 l5. 5 15. 5 15. 5 5 1 5 Hexamethylenetetrainine mononitrate (HMTAMN) 13. 6 13. 0 9. 0 5.0 5. 0 10. 0 2. 5 1- 5 Aluminum 1 17. 0 17.0 Ammonium Nitrate 50. 6 52. 1. Sodium Nitrate 3 14.0 14. 0 1. 4 1. 4 4. 3 5.6 1. 41 1.

1 10 percent granular, 7 percent flake.

2 Prills.

3 Granular to coarse.

4 Cross-linked.

5 Approximately 5,000 grams of slurry is poured into an aluminum funnel having al% diameter x 1 orifice. When the orifice is opened to permit flow, the timing is begun. When light is visible through the orifice (looking down into the tunnel), tuning is stopped. The time The above formulations, and associated data, demonstrate HMTAMN as a sensitizer for inorganic oxidizer salt type blasing compositions of the aqueous slurry type. Thus, formulation 1, containing HMTAMN as the only sensitizer, shot at a rate of 3850 meters per second, whereas formulation 2, substantially the same as formulation 1, except for the absence of HMTAMN, failed to detonate. Formulations 3, 4 and 5, and also 6 and 7, demonstrate variance in sensitizing action of HMTAMN, as measured by detonation rate, that can result from variance in HMTAMN content; formulations 5 and 6 demonstrate a marked variance in sensitizing action (measured with reference to detonation rate) that can be obtained at a constant HMTAMN content level, but which is attributable to significant formulation differences; formulation 8 demonstrates sensitizing action that can be obtained at the low HMTAMN content level of 2 /2 percent, in the absence of a supplemental sensitizer; and formulations. 9 and 10 demonstrate the sensitizing action at a low content of HMTAMN, i.e., below about 5 percent, obtained in conjunction with aluminum as a supplemental sensitizer.

Any suitable process can be utilized for the manufacture of the compositions of the invention. In accordance with one such embodiment, at least a portion of the thickener ingredient is added to, and mixed with, the water to impart suflicient consistency to prevent settling of subsequently added ingredients. The amine nitrate sensitizer is then mixed with the thus thickened water ingredient followed by addition of at least a major portion of the oxidizer salt, advantageously reserving a minor portion for addition with any remaining portion of thickener to be added. After all thickener is added, stirring is continued, preferably at a temperature of 50 to 100 F., for a period of, say, 2 to 10 minutes to form the final product.

In accordance with a now preferred. process for the manufacture of the compositions of the invention, guar gum is utilized as the thickener in conjunction with; HMTAMN as the sensitizer component. The guar gum is initially in hydratable form, e.g., natural guar gum, and constitutes a minor proportion of the total guar gum contemplated and is added with a small proportion of oxidizer salt, for example, about five times its weight of oxidizer salt, to the water, under which conditions the guar gum undergoes hydration to impart consistency to prevent settling of subsequently added ingredients. The resulting thickener-water admixture is maintained at a temperature in the order of, say, 80l00 F. for a period of 2 to 5 minutes after which the HMTAMN, in aqueous solution, and all but a minor proportion of remaining oxidizer salt, as a solid, is added with agitation. The remaining, and major, proportion of the guar gum to be added is crosslinkable and is added with the remaining, and minor,

difference is designated as the flow time.

6 Measured as average detonation velocity over a 20 cm. length, at the end of a 28" long column of explosive. The ex losive is confined 1n 4 diameter (nominal) black iron pipe (Schedule 40 The time for detonation to proceed across the 20 cm. length of explosive is measured electronically by means of a countar-chronograph. In all instances the detonation was initiated by a 475-gram Pcntolite booster charge.

i.e., it contains an agent causing a delay in hydration that would otherwise take place immediately. The delay, or

inhibition, postpones hydration of the last added guar gum so as to permit time for packaging, or emplacement, of the final product mixture while still easily fiowable, with final hydration and cross-linking subsequently taking place.

Various agents contained in the guar gum, and associated conditions for providing the inhibiting and cross linking action above described, are well known. Exemplary agents functioning to inhibit and subsequently promote cross-linking are those which liberate borate, c11- prous, calcium and aluminum ions, the inhibiting and crosslinking being promoted under diiferent pH conditions. For example, sodium borate is often utilized at a pH of from about 5 to 6 to promote inhibition of hydration, and it promotes cross-linking When the pH is increased to about 7. Generally there i suflicient crosslinking agent ultimately present to also cause cross-linking of the already hydrated guar gum initially added. When hexamethylenetetramine dinitrate is utilized as the sensitizer component, and a thickener is utilized, the choice -of crosslinkable thickener is limited to those which can cross-link at a pH in the order of 2.0 and less.

When utilizing a mixture of hexamethylenetetramine mononitrate and hexamethylenetetramine dinitrate, as the sensitizer component, in practice of the invention, the mono and dinitrate can be present in said mixture in any desired proportions.

When referring herein to hydration, it is meant the reaction that takes place between the guar gum and water components to form a sol, and when referring to crosslinking, it is meant the cross-linking reaction that takes place between the guar gum and the particular crosslinking agent to form a gel.

As will be evident to those skilled in the art, various modifications can be made or followed, in light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

What we claim and desire to protect by Letters Patent 1. In an inorganic oxidizer salt explosive of the aqueous slurry type, the improvement comprising a sensitizing amount of a sensitizer component selected from the group consisting of hexamethylenetetramine mononitrate, hexamethylenetetramine dinitrate, and a mixture of said nitrates.

2. A composition of claim 1 containing from 1 to 18 weight percent of said sensitizer component.

3. An aqueous slurry type composition of claim 2 containing on a Weight basis, from 8 to 25 percent water,

40 to 85 percent of said inorganic oxidizer salt, and from 0.2 to 5 percent of a thickener.

4. A composition of claim 3 containing a supplemental sensitizer selected from the group consisting of hydrocarbon oils, finely divided coal, and finely divided metals and metal alloys.

5. A composition of claim 3 wherein said sensitizer is hexamethylenetetramine mononitrate.

6. A composition of claim 5 containing less than about 5 percent of said sensitizer and from 2 to 25 percent of a supplemental sensitizer selected from the group consisting of hydrocarbon oils, finely divided coal, and finely divided metals and metal alloys.

7. A composition of claim 5 containing from 5 to 14 percent of said sensitizer.

8. A composition of claim 7 containing from 12 to 20 5 percent guar gum, in cross-linked form, as said thickener 10. A composition of claim 9 containing finely dlVlCl( aluminum as a supplemental sensitizer.

11. A composition of claim 10 containing less thar about 5 percent of said sensitizer and from about 2 t( 10 25 percent of said aluminum, and said aluminum being at least partially in flake form.

No references cited.

CARL D. QUARFORTH, Primary Examiner.

S. J. LECHERT, IR., Assistant Examiner. 

1. IN AN INORGANIC OXIDIZER SALT EXPLOSIVE OF THE AQUEOUS SLURRY TYPE, THE IMPROVEMENT COMPRISNG A SENSITIZING AMOUNT OF A SENSITIZER COMPONENET SELECTED FROM THE GROUP CONSISTING OF HEXAMETHYLENETGETRAMINE MONONITRATE, HEXAMETHYLENETETRAMINE DINITRATE, AND A MIXTURE OF SAID NITRATES. 